[FFmpeg-devel] patch: the fastest video decoder ever? :)

Paul B Mahol onemda at gmail.com
Fri Jan 6 15:58:08 EET 2017

On 1/6/17, u-9iep at aetey.se <u-9iep at aetey.se> wrote:
> Hello,
> On slow hardware a 16-bit framebuffer depth makes a remarkable difference
> in performance and still provides a good look.
> When videos are to be played on slow terminals there is a single
> best speed performer, cinepak (tell me if you know a better codec in this
> respect, the only comparable one I know of is VQA-15, but there is no
> reasonable encoder for it, nor a safe decoder).
> Unfortunately cinepak as present in ffmpeg yields rgb24 which has to be
> repacked depending on the framebuffer format.
> The attached patch makes cinepak to provide rgb565 in native endianness.
> This cuts in half (!) the mplayer CPU consumption on i686 with Xorg
> in the corresponding mode/depth, compared to decoding to rgb24.
> The optimization is possible because cinepak is a VC codec and pixel
> format packing at codebook fill is much more efficient than at a later
> stage. (Thanks Michael for the suggestion, long ago).
> Of course the picture quality is slightly affected if this decoder version
> is used with larger framebuffer depths. A run-time switch would be to
> prefer, if this optimization against all odds would be welcome upstream :)
> I am posting this as a proof of concept, lacking run-time format
> switching. As said, this patch yields half CPU consumption or double
> speed at decoding for rgb565 terminals.
> Regards,
> Rune

You could easily add option to decoder for picking output format...

See how it is done for encoders.

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